1. SATELLITE REMOTE SENSING OF TERRESTRIAL CLOUDS Alexander A. Kokhanovsky Institute of Remote Sensing, Bremen University P. O. Box 330440 Bremen, Germany alexk@iup.physik.uni-bremen.de

2. Hot issues in cloud research Optical properties of ice and mixed clouds Absorption of solar radiation by clouds Gas-aerosol-cloud interactions 3-D effects in clouds Clouds and climate

3. ENVISAT Start: 28.2.2002

4. SCIAMACHY Instrument Characteristics: UV/Vis/NIR Spectrometer: 240 - 2380 nm Spectral resolution: 0.2 – 1.5 nm 8000 spectral points SCIAMACHY measures: –Reflected solar light (nadir –Reflected solar light (nadir) –Scattered solar light (limb) –Transmitted solar/moon light (occultation) –Solar Irradiance SCIAMACHY = SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY

5. PARAMETERS to be retrieved: Cloud optical thickness /5-100/ Cloud top height /0.5-10km/ Cloud cover /0-1/ Cloud albedo/0.3-0.8/ Liquid water path /50-200 / Thermodynamic phase /ice, water or mixed clouds/ Average size of droplets/crystals

6. The retrieval techniques 1: The look-up-table approach

7. 2: The semi-analytical approach

8. Optical characteristics of clouds Trishchenko and Liu, 2001 Number of cases Optical thickness ISCCP data Surface observations Kokhanovsky, 2003

9. The physics behind the semi-analytical approach SatelliteSun 1 2

10. The cloud optical thickness determination

11. The accuracy of the semi-analytical asymptotic theory

14. Image of Western Europe from Sea-viewing Wide Field of view Sensor 1-km spatial resolution 2001 10 11

15. Retrieved cloud optical thickness distribution

16. Retrieved cloud albedo distribution

17. Frequency distribution: optical thickness

18. Frequency distribution:spherical albedo

19. Hurricane Erin, 1-17 September, 2001 Hurricane Erin grazes Bermuda September 9, 2001 Posted: 11:04 PM EDT (0304 GMT) A satellite photo of Hurricane Erin MIAMI, Florida (CNN) -- Hurricane Erin continued to gain strength Sunday but posed increasingly less threat to land as it strayed farther out in the Atlantic. The worst part of the storm, with maximum sustained winds of 195 km/h, passed to the northeast of Bermuda

20. Hurricane optical thickness distribution

21. Hurricane optical thickness distribution near its eye

22. Hurricane optical thickness distribution in the eye

23. Other applications spherical albedo wavelength, micrometers measurements approximation Experiment/sea foam/, Frouin et al., JGR, C, 2001 Experiment/Antarctic snow /, Grenfell et al., JGR, D,1994

24. Cloud top height determination from a satellite The geometry of the problem

25. Nadir observation, solar zenith angle – 20 degrees Cloud optical thickness –20. The accuracy of the forward model Cloud top height determination from a satellite

26. The accuracy of the forward model Cloud top height determination from a satellite

27. The physical principle behind the retrieval

28. Preliminary results ! Cloud geometrical thickness determination from a satellite

29. Table 1. Characteristics of selected space instruments, related to measurements of the backscattered light in the oxygen A-band (7550-7750 ). InstrumentPlatformYearSpectral interval, Spectral resolution, Spatial resolution, km 2 GOMEERS-219955760- 7940 3.340*320 SCIAMACHYENVISAT20026040- 8050 4.830*60 MERISENVISAT20027600 250.3*0.3 or 1.1*1.1 GLIADEOS-II20027630 80 0.25*0.25 and 1.0*1.0 POLDERADEOS-II20027633 7651 100 400 6.0*7.0

30. Typical SCIAMACHY spectra in the oxygen A-band Cloud top height determination from SCIAMACHY

34. Cloud top height determination from GOME data using oxygen A-band information as compared to ATSR-2 IR retrievals (ERS-2 satellite)

36. Conclusions Most of important cloud parameters can be retrieved using spectral top of atmosphere reflectance. Cases of inhomogeneous clouds can bias retrieval results considerably. This should be clarified in future research. The information on clouds obtained on a global and regional scale should enhance our studies of climate change, including anthropogenic influences on cloud microphysical and optical properties and

37. Clouds are important and

38. Hurricane Erin, Sept 9 th, 2001 Clouds are beautiful!

39. SCIAMACHY Limb profile With NLCs SCIAMACHY Limb profile without NLCs SCIAMACHY observes NLC

40. NLC Season 2002NLC Season 2002/2003 Global detection of NLC with SCIAMACHY

41. Noctilucent clouds Photos: Pekka Parviainen